In semiconductor manufacturing techniques, an inspection of a chip which is processed in a wafer state, has been performed.
When inspecting each chip in a wafer state, electrical operations of the chip on a semiconductor wafer is examined by pressing a probe for inspection to an electrode pad on the chip. At this time, a probe trace is formed on the electrode pad of the chip. There is a technique to determine whether the inspection of the chip is performed properly or not by imaging this probe trace and analyzing the pattern of the probe trace for the obtained image (patent document 1).
To determine whether the inspection is performed properly or not by the probe trace, it is necessary to accurately recognize the image of the probe trace including its position. Normally, the image of the electrode pad is binarized, and the position, shape and size of the probe trace is recognized from the binary image.
The conventional image binarizing method is to set a single threshold value to the entire binary image and binarize the image by using the threshold value. Further, as disclosed in patent document 2, there is a method for binarizing an image by setting a threshold value for each micro region.    Patent document 1: Japanese Unexamined Patent Application Publication No. 2005-45194.    Patent document 2: Japanese Unexamined Patent Application Publication No. H4-78969.